Electric cutout



United States Patent O ELECTRIC CUTOUT William Irby, Saugus, Mass., assignor to General Electric Company, a corporation of New York Application June 12, 1952, Serial No. 293,149

7 Claims. (Cl. 20G-118) My invention relates to electric cutouts for series circuits and to methods of making the same, and more particularly to copper oxide cutouts having a narrow range of probable voltage breakdown. This application is a continuation-impart of my co-pending application Serial No. 218,966, filed April 3, 1951, and now abandoned.

Series cutouts are normally insulating or dielectric elements having predetermined voltage breakdown characteristics and connected in shunt circuit relation with electric devices in series circuits, whereby upon open circuiting of any such electric device, such as an incandescent lamp, the associated cutout breaks down and passes current in shunt around the defective device to maintain the continuity of the circuit for operation of the other series connected devices. Copper oxide cutouts are commonly formed as wafers of copper coated on both sides with layers of cuprous oxide and overlying layers of cupric oxide. Such an oxidized wafer provides a copper-tocuprous oxide junction on each face. The electric resistance of each such junction is high for current passing from the copper to the cuprous oxide, and low for current passing from the cuprous oxide to the copper.

When such an oxidized wafer is placed in an electric circuit with Contact made to the two oxidized outer faces, the wafer serves as a blocking rectifier for current in either direction, since the wafer is in effect a pair of copper rectiers connected in series circuit opposition.

Such copper oxide cutouts are commonly used in series lighting circuits, both A. C. and D. C., by connecting a cutout across the terminals of each lamp. The cutout normally passes no current in either direction except a very small leakage current, but if a lamp burns out, the high voltage across the lamp terminals breaks down the associated cutout and the cutout shunts the lamp, thereby maintaining operation of the other lamps in the circuit.

Heretofore diiculty has been experienced in so forming copper oxide cutouts that the breakdown voltages of all of a representative group of cutouts could be maintained Within a predetermined narrow voltage range. lndividual cutouts, although taken from the same batch and operated under similar conditions, have demonstrated breakdown voltages varying over a wide range, the maximum voltage breakdown being more than twice the minimum voltage breakdown. Such wide variation in voltage breakdown characteristics is further aggravated when the cutouts are subjected to unusual conditions of temperature and humidity. In an effort to remedy these conditions it has heretofore been proposed that the cutouts be formed from copper containing traces of another metal, such as silver, but it has been found in practice that the voltage breakdown distribution curve for such silver-bearing cutouts, while comewhat more peaked or concentrated than for cutouts containing no intentional impurity, still covers a very wide voltage range from minimum to maximum breakdown voltage. It is, of course, obviously desirable that electric cutouts of any predetermined voltage rating shall possess voltage breakdown characteristics which fall within a relatively narrow voltage range. It is further desirable that the voltage breakdown characteristics be reasonably unaffected by varying conditions of temperature pressure and humidity, experienced in operation.

Accordingly, therefore, it is a general object of my invention to provide electric cutouts having a distinctively narrow range of probable voltage breakdown.

It is another object of my invention to provide copper oxide cutouts having voltage breakdown characteristics which are confined to a narrow range of voltage.

meice Another object of my invention is to provide copper oxide cutouts the voltage breakdown characteristics of which are not appreciably affected by temperature, humidity or the mechanical pressure imposed by mounting prongs and the like in operation.

It is still another object of my invention to provide copper oxide cutouts having a narrow range of probable voltage breakdown and demonstrating a very low resistance to current flow after breakdown.

A further object of my invention is to provide a method for making copper oxide cutouts having the foregoing characteristics.

In carrying out my invention in one form I attain the foregoing and other objects by forming copper oxide cutouts from copper wafers which have been alloyed at least at their surfaces with certain other metals prior to firing or oxidation. Such an alloy may suitably be formed by coating the copper surface with thin films of iron and antimony, the iron and antimony alloying with the copper at the surface when the coated wafer is exposed to an oxidizing atmosphere at elevated temperature. Before firing, however, the copper wafer coated with iron and antimony is dipped in a dilute solution of certain salts. Such a solution preferably includes a soluble salt of antimony, a tetraborate, an iron nitrate and an organic acid. After such dip, and before the wafer is dried, it is inserted in an oxidizing furnace, thereby to form upon opposite faces undercoatings of cuprous oxide and outercoatnigs of cupric oxide. After firing the oxidized wafers are allowed to cool in air.

My invention itself will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. l shows a cutout assembled in a protective jacket and disposed in operating relation between the prongs or terminals of a series circuit socket; Fig. 2 is a cross-sectional view of the cutout assembled in its protective casing; and Fig. 3 is a comparative graphical representation of certain significant voltage breakdown distribution data taken for a representative group of my improved cutouts and for similar representative groups of certain cutouts made by prior methods.

Referring now to the drawing in detail, I have shown at Fig. l a pair of electric conducting terminal prongs 1 and 2 of the type forming part of a typical series circuit socket (not shown) supporting between them a cutout 3 assembled in a protective casing. A complete socket of this type is shown in Patent 1,813,799-Halvorson- Fig. l includes also a simple schematic illustration of a series lighting circuit including a supply transformer 4 and a plurality of lights 5, 6 and 7, the cutout 3 being connected across the light 6.

At Fig. 2 l have shown a cross-sectional View of the assembled cutout 3. The cutout comprises a copper oxide wafer 8 coated on opposite faces with cuprous oxide and assembled between a pair of metal terminal plates 9 and 10 within a protective casing formed by crimping over the edges of the terminal plate 9. The assembly of such a cutout is more clearly described and claimed in Patent 2,059,890-Myers.

The oxide coated wafer 8 is formed by rst cleaning and then etching in a dilute water solution of nitric acid a thin copper disk or wafer. After etching the disk it is thoroughly rinsed, and is then coated with iron to form, on opposite faces of the disk a very thin iron film. Preferably the iron coating is carried out in an electrolytic plating bath for about 21/2 seconds at a current density of 18 amps. per square foot, or the equivalent in ampere seconds per square foot. The iron coated copper disk or wafer is then again rinsed and a thin film of antimony is applied to the iron plated surface. Preferably the antimony coating is also carried out in an electrolytic plating bath, the plating being carried on for about ten seconds at a current density of about 30 amps. per square foot, or the equivalent in ampere seconds per square foot.

After a final rinse following the antimony plating the plated wafer is then dipped in a dilute solution (for example, less than 1% concentration) of a soluble salt of antimony. Preferably such a solution includes also a small amount of a tetraborate, a quantity of iron nitrate, and an organic acid to stabilize the antimony salt and hold it in solution. One particular solution which I have found to be satisfactory consists of by weight .5 antimony chloride, .05% sodium tetraborate, .1% ferric nitrate, about 3% tartaric acid and the remainder water. I find that certain other salts are also effective as a prefiring dip. In general the nitrates and perchlorates as well as the chlorides and other halides (i. e., iiuoride, bromide or iodide) of antimony, bismuth or iron have significantly beneficial results. I prefer, however, to utilize the foregoing solution of antimony chloride and iron nitrate. The tartaric acid in my preferred solution serves principally to increase the amount of antimony chloride held in solution. The sodium tetraborate serves principally as a cleaning flux.

After dipping the iron and antimony coated wafer in the solution described above, and before the dipping solution has dried, the wafer is oxidized or "fired to form on opposite faces thereof a coating of cuprous oxide. Preferably the firing operation is carried out in a furnace wherein the wafers are exposed to air or other oxidizing atmosphere at a temperature of about 1800 F. to 1900 F. for an interval of about to 20 minutes. In this operation the iron and antimony coatings are first alloyed with the copper wafer, and thereafter layers of cuprous, or red oxide are formed under thin overlying films of cupric, or black, oxide. After oxidation the wafers are cooled to room temperature in air and then stripped by tumbling in a dilute solution of sulphuric acid. This tumbling operation removes the black oxide.

After the foregoing acid cleaning the oxidized wafers are rinsed in clear water and dried in air. The cleaned and dried wafers are then annealed, preferably in an annealing furnace, at about 950 F. to 1050 F. for a period of approximately 10 to l5 minutes. After annealing the wafers, for certain voltage ratings, are allowed to cool in air at room temperature and are then ready for test or use as desired. For other voltage ratings the wafers are quenched in water immediately after annealing. The breakdown voltage range may also be controlled to some extent by varying the firing time or the annealing time, or both.

It will be understood from the foregoing process, when the metal plated and dipped wafers are subjected to the firing operation the very thin surface films of iron and antimony are first alloyed with the copper before the copper itself is oxidized to form cuprous oxide. Thus it will be evident to those skilled in the art that the same effect may be obtained and the advantages of my invention realized by subjecting to the firing operation a copper wafer, at least the opposite faces of which have had antimony and iron alloyed therewith in any desired manner prior to firing. For example, antimony and iron bearing copper may be fired directly without the preceding metal plating operation. Similarly, it will be understood by those skilled in the art that even if it is desired to utilize iron and antimony films on an unalloyed copper wafer and then fire the coated wafer as described, it is not essential that the iron and antimony iilms be deposited electrolytically. Other suitable methods may be utilized for coating the faces of the copper wafer with iron and antimony prior to firing.

Copper oxide cutouts formed by my foregoing new and improved process demonstrate much more favorable voltage breakdown characteristics than do cutouts commonly formed heretofore in a similar manner but without the metal plating and dipping prior to tiring. In the first place, the probable range of voltage breakdown for any representative group of cutouts is distinctively narrowed when the cutouts are formed by my new and improved process. This is illustrated at Fig. 3, where I have graphically illustrated the comparative results of voltage breakdown tests on three similar groups of cutouts, one group being formed by the oxidation of pure copper (i. e., no intentional impurity introduced), another group being formed from silver-bearing copper, and the third group being formed by my above-described plating and predipping method. On the curves at Fig. 3 the abscissas represent breakdown voltage, the indicated design range being between 100 and 200 volts, and the ordinates represent the number of cutouts in each group which were found to break down at the various voltages. It will be evident from inspection that the distribution curves shown for pure copper and for silver-bearing copper indicate a wide range of probable voltage breakdown and no clear tendency of the cutouts as a group to break down at any well defined voltage. On the other hand, the voltage breakdown distribution data for that group of cutouts formed by my predipping and plating method, above-described, indicate that all the cutouts in the group broke down within a range of about 20 volts between minimum and maximum breakdown. The breakdown voltage of such cutouts is therefore more definitely predictable, and the likelihood of failure by breakdown outside the desired design range is virtually eliminated.

I have found in addition that the narrow range of probable voltage breakdown in my new and improved copper oxide cutouts is very nearly independent of temperature. This is a very desirable characteristic, since all cutouts operate normally between and 200 C. both because of leakage current heating and because of their usual location near the socket of an incandescent lamp. I have found also that the breakdown voltage of my improved copper oxide cutouts is very little affected by varying humidity conditions and is nearly independent of mechanical pressure applied to the cutouts in operation, as by the mounting prongs l and 2 of Fig. 1. Finally I have discovered that cutouts formed in accordance with my invention run at lower temperatures after breakdown than has heretofore been obtainable. Such low temperature operation after breakdown indicates that the rupture of the blocking layer is very complete, so that no undesirable resistance is introduced into the circuit by the ruptured cutout.

While I have described only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art, and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making copper oxide cutouts having a narrow range of probable voltage breakdown which comprises alloying iron and antimony with at least the opposite surfaces of a copper wafer, dipping the wafer in a dilute water solution containing less than 1% by Weight of antimony chloride, and exposing the wafer to an oxidizing atmosphere at elevated temperature thereby to form on opposite faces thereof coatings of cuprous oxide.

2. The method of making copper oxide cutouts having a narrow range of probable voltage breakdown which comprises forming sequentially on each face of a copper wafer a thin film of iron and a thin film of antimony, dipping the wafer in a dilute water solution containing less than 1% by weight of antimony chloride, and exposing the wafer to an oxidizing atmosphere at a temperature which will alloy said films of iron and antimony with said copper wafer and form on opposite faces thereof coatings of cuprous oxide.

3. The method of making copper oxide cutouts having a narrow range of probable voltage breakdown which comprises forming sequentially on each face of a copper wafer a thin film of iron and a thin film of antimony, dipping the coated wafer in a dilute water solution containing by weight about .5% antimony chloride and about .1% ferrie nitrate, and exposing the wafer to an oxidizing atmosphere at about 1800 F. to 1900 F. thereby to form upon said faces coatings of cuprous oxide.

4. The method of making copper oxide cutouts having a narrow range of probable voltage breakdown which comprises in the order stated electrolytically depositing sequentially upon each face of a copper wafer a thin film of iron and a thin film of antimony, dipping the coated wafer in a dilute water solution containing by weight about .5 antimony chloride, .05% sodium tetraborate, .1% ferric nitrate, and 3% tartaric acid, exposing the wafer to an oxidizing atmosphere at about 1800 F. to l900 F. for a period of about 15 to 20 minutes thereby to form upon said faces coatings of cuprous oxide, cooling the oxidized wafer to room temperature in air, stripping from the surface of the cuprous oxide on the Wafer any cupric oxide formed during said preceding operations, annealing the wafer at about 900 F. to 1050 F. for a period of about 10 to 15 minutes, and then immediately cooling the wafer to room temperature.

5. A cutout for electric circuits comprising a wafer having a face of copper alloyed with antimony and iron and a layer of cuprous oxide on said face.

6. A cutout for electric circuits comprising a wafer of copper alloyed with traces of iron and antimony and coated on opposite faces with layers of cuprous oxide.

7. A cutout for electric circuits comprising a copper wafer coated on opposite faces with cuprous oxide and having iron and antimony alloyed with the copper and cuprous oxide at least immediately adjacent the coppercuprous oxide junction on each side of the wafer.

References Cited in the le of this patent UNITED STATES PATENTS Geiger Dec. 1, 1931 Ackerly Sept. 12, 1933 Friedrich May 18, 1937 Meyers, Jr. Oct. 26, 1937 Hartz May 24, 1938 Taylor Sept. 24, 1940 Doucet Nov. 4, 1941 Dowling Sept. 7, 1943 Taylor Apr. 15, 1952 

